Reactive materials, including alkali metals such as rubidium and cesium, have many applications in industry. For example, one type of atomic clock utilizes a vapor cell containing an active medium of rubidium or cesium vapor that is simultaneously irradiated with light from a microwave signal and an optical source such as a laser. The optical source pumps the rubidium or cesium atoms from a ground state to a higher state from which they fall to an energy state which is at a hyperfine frequency different from the initial ground state. This causes the rubidium or cesium atoms to absorb energy at a microwave frequency corresponding to transitions between the two hyperfine levels of the ground state. It is desirable to have the longest amount of time possible to measure the energy levels of such atoms. One way to obtain a long measurement time is to keep the atoms in one place while measuring them. The vapor cell does this by containing the rubidium or cesium atoms in the vapor cell. Generally, such vapor cell structures provide a vacuum environment, such as a vacuum chamber, so that the behavior of the relatively small number of the rubidium or cesium atoms in the vapor cell can be measured with minimal interference from other materials.
In order to manufacture atomic clocks that are small, portable and highly accurate and have low power requirements, it is necessary to decrease the size of the various components of the atomic clock, including the vacuum chamber. However, as the size of the vacuum chamber is decreased, the problem of contamination that interferes with the measurement of the behavior of the relatively small number of rubidium or cesium atoms in the vacuum chamber increases.